Applicator for liquid chemical conversion coating material



W- S. HALL Feb. 17, 1910 APPLICATOR FOR LIQUID CHEMICAL CONVERSION COATING MATERIAL Filed July 5, 1967 INVENTOR. Jam ,1. M BY Arrow/Er:

United States Patent 3,495,570 APPLICATOR FOR LIQUID CHEMICAL CONVERSION COATING MATERIAL Wilbur S. Hall, Plymouth Meeting, Pa., assignor to Amchem Products, Inc., Ambler, Pa., a corporation of Delaware Filed July 3, 1967, Ser. No. 650,898 Int. Cl. B05c 11/00 US. Cl. 118-267 6 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a brush-type applicator for applying chemical conversion coating material to a moving metal surface in a manner to obtain a uniform film of the conversion liquid on the metal, and hence, a uniform conversion coating on the metal both across its width and along its length. The brush applicator includes a generally fiat brush, a feed reservoir mounted to feed a uniform stream of conversion coating material to the filaments of the brush across its width, capillary type feed means between the reservoir and the brush filaments, and mounting means for holding the brush in coating contact with a metal surface being moved past it.

This invention relates to the art of applying liquid chemical conversion coating materials to metal surfaces, and particularly to moving metal surfaces such as those encountered in operations where long coils or strips of metal are coated in equipment which conveys the strip past a station at which the conversion coating material is contacted with the metal. The invention is especially concerned with a brush-type applicator for applying a liquid chemical conversion coating material to a moving metal surface in a uniform manner.

In the coating of a long strip of metal, uniformity of conversion coating weight is an important goal, for several reasons. If there is a variation in the Weight per unit area of the coating, either across the wid h of the long strip, or along its length, there may be a substantial variation in the paint adhesion and corrosion resistance properties of the treated surface, such variations being undesirable. Even when there is a relatively slight change in performance properties when the coating weight varies, it is desirable for economic reasons to produce a uniform coating. Thus, if a coating application apparatus which inherently applied a nonuniform coating is employed, it must be adjusted so that the minimum coating it applies adequately meets the coating performance requirements. Other areas of the coated metal will inevitably have coatings which are heavier, sometimes far heavier, than needed, and such heavily coated areas represent a waste of coating material.

The most feasible approach to the achievement of uniform coating is to take steps to insure that a uniform film of coating liquid is applied to all areas of the metal surface being coated. The applied film of liquid should be uniform both across the strip of metal and along its length. Thus, when a strip of metal is being moved at a steady rate past a coating station, it is important that the volume of liquid applied per unit of time to the strip be consant in order to obtain uniformity of liquid film, and hence, uniformity of coating along the length of the strip. Additionally, the volume of liquid applied across each inch of width of the strip should be uniform in order to ob ain uniformity of applied liquid film, and uniformity of final coating, across the width of the strip. In general, the wider the strip, the more difiicult it is to achieve such uniformity.

3,495,570 Patented Feb. 17, 1970 ice While the problems involved in obtaining uniform coating weights on long strips of metal are capable of relatively simple analysis and definition, as in the above discussion, the achievement of uniform coating weight has proved quite difficult. Heretofore, spray systems have been widely employed. Such systems are complex, difiicult to stabilize, and require extensive maintenance. Various roll coating systems of application have been used, the most successful being those described in US. Patents 3,098,775, and 3,215,564. However, such equipment requires a considerable capital investment (as does spray equipment), and the frequent adjustments of such equipment necessary to maintain uniform coating weight require the service of a skilled mechanic.

Attempts have also been made to adapt techniques which have had some measure of success in the field of applying paints and other siccative finishes to metals. Thus, pressure fed felt rollers have been tried, and brushes having pressure feed to the head of the brush have been tried. However, since the viscosity and flow properties of conversion coating liquids are considerably different than these properties for paints, such attempts have been unfruitful.

In accordance with this invention it has been discovered that a uniform film of conversion coating liquid can be applied to a moving strip of metal by means of a brush applicator having a special feed system in which uniformity of feed is imposed by utilizing capillary flow both in the feed of the liquid to the brush applicator and in the flow of liquid through the brush applicator from the point of feed to the point of application to the metal.

The preferred means by which capillary control of flow rate is achieved include a reservoir positioned near the upper end of the brush applicator for holding a supply of conversion coating liquid. The reservoir extends substantially all of the way across the brush, and is configured so that it will hold substantially equal volumes of conversion coating liquid above each increment of width of the brush.

Interposed between the reservoir and the upper end of the brush are means establishing a narrow slot-like flow passage substantially as wide as the brush and the reservoir, but of relatively narrow thickness. The structure just described is one in which the rate of flow of liquid throughout the width of the passage is determined principally by the dimensions of the passage and the properties of the surfaces defining the passage, and is influenced to only a minor extent by variations in the head of liquid in the reservoir.

One form of variation in head in the reservoir can occur when only a small amount of liquid is being maintained in it, and the rate of feed of liquid into the reservoir is barely sufiicient to match the rate of feed out of it. Under such conditions the head near the point of introduction of liquid into the reservoir will tend to be higher than the head at points remote from the feed point. Another type of variation in head occurs when the rate of feed of liquid into the reservoir varies with time, as it normally will. When the rate of feed into the reservoir exceeds the rate of flow out, the head will tend to rise, and when it is less than the rate of feed out, the he d will tend to fall.

The term capillary flow has been used above, and will be used throughout this application, to refer to liquid flow of the kind occurring in the flow passage just described. That is, capillary flow refers to flow under conditions where the structure of the flow passage is the main determinant of the flow rate, or at least a more significant determinant than is the head of liquid upstream from the region of capillary flow, i.e., in the reservoir.

In this connection, it should be pointed out that the applicator of the present invention can be operated with the slot-like flow passage thickened to such an extent that the head of liquid in the feed reservoir has an appreciable effect on the rate of flow. But even under these circumstances the structure of the flow passage will tend to moderate variations in flow rate caused by variations in head, and satisfactory operation can be achieved if care is taken to keep the level of liquid in the reservoir as uniform as possible.

The capillary fiow passage just described delivers the liquid flowing through it to the brush itself. In the preferred arrangement, the point of delivery to the brush is at one side thereof near the upper end, and the brush slopes downwardly to sliding contact with the metal surface being treated. The closely packed filaments of the brush constitute a structure establishing a multiplicity of capillary flow passages extending from the point of delivery of liquid to the brush downwardly to the surface of the brush. These flow passages, like that of the slot-like flow passage described above, are configured so that the rate of flow through them is determined principally by their size and shape, and by the surface properties of the filaments. Furthermore, in the brush structure the capillary flow passages formed by the filaments are substantially uniform, one with another, across the width of the brush.

Thus it can be seen that, in accordance with the invention, two capillary fiow systems are interposed in series with each other between the reservoir of coating liquid and the surface to be coated. Each of these capillary flow systems tends to promote uniformity of application of liquid to the surface being treated by establishing uniformity of liquid flow both across the width of the surface, and With respect to time, and each tends to minimize effects of variations in feed head. The combined effect of these two capillary flow systems in series is the achievement of substantially complete uniformity of application of coating liquid to the surface contacted by the brush.

It is an object of this invention to provide improved means for applying a uniform film of liquid conversion coating material to a metal surface, to thereby form on the surface a uniform conversion coating.

Another object of the invention is the provision of a simple and inexpensive brush-type device for applying liquid chemical conversion coatings to surfaces.

A further object of the invention is the provision of a brush-type applicator for applying liquid chemical conversion coating material to a metal surface, which applies such material uniformly, without need for frequent or complex adjustment to maintain such uniform application.

The foregoing objects, together with other objects, may be more readily understood by a consideration of the detailed description which follows together With the accompanying drawing in which:

FIGURE 1 is a somewhat diagrammatic side elevational view of a brush applicator of the invention shown in use applying a film of conversion coating material to a moving metal strip;

FIGURE 2 is a side elevational view, partly in section, on an enlarged scale compared with FIGURE 1, of a brush applicator constructed in accordance with the invention, the section being taken approximately on the line 22 of FIGURE 3; and

FIGURE 3 is a plan view of the brush applicator of FIGURE 2, with parts broken away.

Before considering the device shown in the drawings, it should be pointed out that it is capable of use with a variety of chemical conversion coating formulations, and that this term is accordingly used here in its broad sense. Among the types of solutions for which the invention is particularly suitable are the chromate conversion coating solutions, employed on aluminum such as those disclosed in US. Patent 2,796,370, and chromate conversion coating solutions of the kind used on galvanized iron and steel. 7

Turning now to FIGURE 1, there is provided in accordance with the invention a brush applicator designated generally as 10. It is mounted above a strip of metal 11 which is to be coated. As FIGURE 1 is drawn, the metal strip 11 is moved at a uniform rate from right to left, past, and generally beneath, the brush applicator 10, this movement being indicated by arrow 12. The movement of metal strip 11 is accomplished by power driven roll 13, upstream from the brush applicator 10, and by power driven squeegee rolls 14, downstream from the applicator. Other means for moving the strip past the applicator may be employed if desired. While the brush applicator 10 will be discussed in greater detail in connection with FIG- URES 2 and 3, it can be pointed out, in connection with FIGURE 1, that it includes a brush portion 15, reservoir means 16, and mounting means 17. The reservoir means 16 includes an upward extension 18 to increase the liquid capacity of the reservoir. Conversion coating liquid is fed into the reservoir through feed line 19 by means of pump 20, which draws liquid from a feed tank or drum (not shown).

A uniform film 21 of conversion coating liquid is placed on the moving surface 11 by the brush applicator 10, the line of application being the tip or edge of brush portion 15. The space between the tip of brush l5 and the squeegee rolls 14 provides a dwell period for the conversion coating film on the metal surface, during which dwell period the liquid film reacts with the surface to form the coating. When the strip 11 is moved at a uniform speed, the time length of the dwell period for each increment of metal is uniform.

FIGURE 2 shows the brush applicator on an enlarged scale. In this figure it can be seen that the brush portion 15 is made up of a plurality of bristles 22 arranged in a generally rectangular pack and secured in such a pack by brush head 23. The brush is thus generally flat, and as can be seen best in FIGURE 3, the free ends of the bristles 22 define a generally straight edge marked 24 at the surface of the metal strip 11. FIGURE 3 also shows that in the preferred embodiment the width of the brush portion 15, measured across its fiat dimension, is substantially the same as that of metal strip 11. For most purposes, this arrangement is preferred, since the goal of the coating operation is usually to place a coating on the full width of the strip. In those instances where a coating is not required on the full width of the strip, a correspondingly narrower brush portion can be employed. The bristles or filaments of the brush portion should be resistant to the action of the conversion coating liquid.

One important advantage of a brush-type element for applying conversion coating liquid is that it automatically adjusts to minor variations in position of the metal strip and to minor surface irregularities, because of its inherent flexibility.

A base piece 25 is bolted to the brush head 23 by bolts 26. The base piece 25 has the shape of a triangular prism, with one side positioned against the upper fiat side of the brush head 23 and the upper end of the brush portion 15 Base piece 25 is provided with a bore through which mounting rod 27 is passed. At each end of the mounting rod 27 are mounting arms 28, which arms are arranged in a conventional manner for adjustable up and down movement. As the arms are adjusted upwardly or downwardly, the angle of the brush applicator with respect to the strip of metal 11 changes. The angle between the applicator and the strip can be varied bet-ween about 10 and about with the preferred angle being about 45. The relative positions of mounting rod 27 for brush angles of approximately 10 and 80 are shown in dotted outline at 27' and 27" on FIGURE 2, while the applicator is shown in all figures at the preferred position of about 45.

A reservoir piece 29 is fastened to the one side of base piece 25 by means of studs 30 and wing nuts 31. Like the base piece 25, reservoir piece 29 is somewhat wider than the brush portion 15, and the bottom surface 32 of piece 29 is shaped to bear against the brush portion 15. Surface 32 tends to prevent the brush from bowing out unduly as the metal surface 11 moves past it.

The reservoir piece 29 is partially hollowed out at 33 to form the conversion coating liquid reservoir 16. The reservoir 16 is defined by the sloping floor 34 and end walls 35, which are formed in reservoir piece 29, and by vertical wall 36 of base piece 25. As mentioned above, the liquid holding capacity of reservoir 16 can be augmented by reservoir extension 18, which is shown broken away in FIGURE 3.

Capillary flow passage 37 extends from the bottom of reservoir 16, where sloping floor 34 meets vertical wall 36, to the side of brush portion at 38, near the upper end thereof, but spaced from brush head 23 a distance sufficient to preclude interference with liquid flow by brush head 23. Capillary flow passage 37 is slot-like in configuration and extends for substantially the full width of reservoir 16 and for the full width of brush portion 15. The flow passage 37 is defined by parallel wall elements 39 and 40, wall element 39 being a vertical side of reservoir piece 29, and wall element 40 being a vertical side of base piece 25. The ends of slot-like passage 37 are formed by spacers 41 discussed below.

In order to form and maintain the shape of flow passage 37, it is necessary that wall elements 39 be held in parallel opposed spaced relationship when base piece 25 and reservoir piece 29 are assembled together. To this end, the outboard portions of base piece 25 are cut away, as at 42, to accommodate the above mentioned spacers 41. The spacers 41 are preferably formed of a resilient material resistant to the action of the conversion coating solution, and, as can be seen in FIGURE 3, are somewhat thicker than cut away portion 42 of base piece 25. When reservoir piece 29 and base piece 25 are assembled together by means of studs 30 and wing nuts 31, the spacers 41 are compressed to the desired extent. The amount by which the compressed thickness of spacers 41 exceeds the thickness of the cutouts 42 in base piece 25 determines the thickness of slot-like flow passage 37. As appears most clearly from FIGURE 2, the spacers 41 have a height equal to the height of base piece 25. Thus, the spacers 41 form both the end walls of slot-like passage 37, and a very small portion of the end walls of reservoir 16. As mentioned above, it is preferred that the spacers be resilient so that the thickness of passage 37 can easily be adjusted by tightening or loosening wing nuts 31. How.- ever, if such adjustability is not required in a given installation, the spacers need not be resilient.

With the above description of the structure of the invention at hand, its mode of operation can now 'be summarized. The brush applicator is initially positioned at the desired angle above the strip 11. The reservoir 16 is filled with conversion coating liquid and after the brush is thoroughly wet, the strip 11 is placed in motion past the brush at a uniform rate. Pump feeds conversion coating liquid into the reservoir 16 at a rate which approximates the rate of consumption as nearly as possible, thereby establishing a head of liquid in the reservoir 16 which is as uniform as possible. A slot-like stream of liquid flows through slot-like passage 37 downwardly out of the reservoir 16. The rate of flow is determined principally by the size and shape of the passage 37, and the rate of flow of the stream is substantially uniform throughout the width of passage 37, and also with respect to time. The stream of liquid flowing through passage 37 is intercepted by brush portion 15 of the applicator, and the liquid in the stream is distributed into a multiplicity of capillary flow passages formed by the filaments of the brush. The liquid flows downwardly through the brush by capillary action in a series of streams, which, when integrated, yield a uniform application of the liquid to strip 11 at the edge 24 of brush portion 15.

I claim:

1. A brush applicator for applying a liquid chemical conversion coating to a metal surface being moved past said applicator, comprising: a brush portion comprising a plurality of bristles arranged in a generally rectangular pack having a width substantially equal to the width of the area to be coated by means of said applicator, said applicator further comprising reservoir means mounted adjacent said pack of bristles at one side thereof, said reservoir means having an adjustable capillary feed passage therein communicating with the side of said pack of bristles and extending substantially across the width thereof, means for changing the thickness of said adjustable capillary feed passage, and mounting means for orienting and holding said brush portion at an acute angle with respect to said metal surface wtih the free ends of said bristles facing in the direction of movement of said surface, and in contact therewith, and with said reservoir means located generally above said surface and above said pack of bristles.

2. A brush applicator for applying a liquid chemical conversion coating to a metal surface being moved past said applicator, comprising: a generally flat bristle brush having a bristle securing head and in which the free ends of the bristles define a generally straight edge, reservoir means for holding and feeding to the brush a supply of liquid chemical conversion coating material, said reservoir means being positioned at a flat side of the brush adjacent the bristles thereof, and extending substantially across said flat side, said reservoir means being provided with a capillary feed passage therein communicating with said brush bristles along a line extending substantially across the flat side of said brush, said line being spaced from said brush securing head, adjusting means for changing the size of said feed passage, and mounting means for holding said applicator in brushing contact with the moving metal surface being coated at an acute angle thereto with said reservoir means above said brush.

3. An applicator for applying a liquid chemical conversion coating to a selected width of a metal surface being moved past said applicator, comprising: conversion coating liquid reservoir means positioned above said moving metal surface and generally orthogonally to the direction of movement thereof, said reservoir means having a width at least substantially equal to said selected width, a multiplicity of closely packed filaments positioned beneath said reservoir means and extending downwardly at an angle to sliding contact with said moving metal surface, and capillary feed means beneath said reservoir means and between said reservoir means and said filaments for feeding conversion coating liquid generally downwardly out of said reservoir in a stream extending substantially across the width of said reservoir means, said capillary feed means including a substantially uniformly sized passage from said reservoir means extending substantially across the width thereof, to establish a substantially uniform rate of flow throughout the width of said stream, said filaments intercepting said capillary feed means passage and the stream of liquid passing therethrough, and said filaments establishing a multiplicity of substantially uniform capillary flow paths extending downwardly from said feed passage to said moving metal surface.

4. A brush applicator for applying a liquid chemical conversion coating to a metal surface being moved past the applicator, comprising a bristled brush mounted above and in position to engage the metal surface and at acute angle to the surface, the brush being of width corresponding to the width of the surface to be coated, and mechanism for feeding said liquid to the brush including a liquid reservoir extended across the width of the brush and a pair of parallel spaced and opposed wall elements below the reservoir positioned to define a slot-like flow passage extended throughout the width of the brush and being in communication with the reservoir alOng the upper edges of said pair of wall elements, and said pair of wall elements being extended to a position adjacent the upper side of the brush so that the outlet of the flow passage delivers said liquid substantially directly to the bristles of the brush.

5. A brush applicator for applying a liquid chemical conversion coating to a metal surface being moved past said applicator, comprising: a brush portion comprising a plurality of bristles arranged in a generally rectangular pack having a width substantially equal to the width of the area to be coated by means of said applicator, and a brush head enclosing one end of said pack of bristles across the width thereof and securing the bristles in packed relationship, a base piece attached to said brush head at one side thereof, and extending along one side of said pack of bristles toward the free end thereof a selected distance; a reservoir piece attached to said base piece, and positioned adjacent said one side of said pack of bristles, said reservoir piece having a hollowed out portion therein adjacent said base piece, said reservoir piece further having a surface lying adjacent said pack of bristles and extending toward the free end thereof; spacer means positioned between said base piece and said reservoir piece for holding said pieces a selected distance apart to thereby define a capillary fiow passage extending from said hollowed out portion of the reservoir piece to said pack of bristles;

and mounting means for orienting and holding said brush i portion at an acute angle with respect to said metal surface, said mounting means being attached to said base piece.

6. An applicator for applying liquid chemical conversion coating to a metal surface being moved past said applicator comprising reservoir means for holding a supply of liquid chemical conversion coating material, first capillary feed means and second capillary feed means cooperating to provide a uniform rate of liquid flow from said reservoir means to said moving metal surface, said second capillary feed means comprising a plurality of bristles arranged in a generally rectangular pack having a width substantially equal to the width of the area of said metal surface,v to be coated, said reservoir means being positioned adjacent and above said first and second capillary feed means, said first capillary feed means positioned between said reservoir means and said second capillary feed means to feed said liquid from said reservoir means onto said second capillary feed means at points substantially across the width thereof, and the flow of liquid from said reservoir means to said first capillary feed means being downwardly out of the reservoir means and extending substantially across the width thereof.

References Cited UNITED STATES PATENTS 2/1933 Krueger et al. 1l8268 XR 3/1936 Riterfeld 118267 

